1. Field of the Invention
The invention relates generally to scanning antennas and, in particular, to apparatus for automatically stabilizing the beam pointing accuracy of a scanning phased array antenna.
2. Description of the Prior Art
Scanning antennas, and, particularly, phased array antennas such as are found in microwave landing systems, have used slotted waveguides that monitor the aperture of the antenna. In phased arrays, biasing error is independent of the angle in space. In contrast, the angle error in beam port antennas is angle dependent. Typically, these waveguides are weakly coupled to the aperture and could be used to manually detect the array beam pointing bias error caused by RF phase perturbations in the antenna circuitry such as from temperature changes, temperature gradients and component degradation and replacements.